A method for preparing ultra-loose sandstone samples and testing long-distance particle migration

Abstract

The present invention discloses a method for preparing ultra-loose sandstone samples and testing long-distance migration of particles, comprising: freezing a core sample; setting a double-layer seal at both ends of the core sample; setting a polyethylene heat shrink sleeve outside the aforementioned structure and heating to obtain an oil-washing sample; washing the oil-washing sample; drying the oil-washing sample after washing, setting an elastic shrinkage device at the injection end to obtain a displacement sample; displacing the displacement sample, collecting the primary production water at the production end until no more particles are produced, and testing the particle size distribution of the particles in the primary production water; re-injecting the primary production water into the displacement sample, collecting the secondary production water at the production end until no more particles are produced, and testing the particle size distribution of the particles in the secondary production water after reinjection, that is, obtaining the long-distance particle migration law. The present invention provides a new method with better effect for studying the long-distance particle migration law in the development process of old oil fields, which is of great significance for the economic and efficient development and utilization of oil reservoirs.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development research, and particularly relates to a method for preparing an ultra-loose sandstone sample and testing long-distance particle migration. Background Art

[0002] Particle migration within oil and gas reservoirs is a common phenomenon during oil and gas development and is considered a major cause of reservoir permeability impairment and reduced oil and gas production capacity. Reservoir particles sometimes appear as fillers dispersed within intergranular pores, sometimes not firmly bound by natural cements within the rock, and sometimes even appear as loose particles on pore walls or the inner surfaces of skeletal particles. Mechanisms of reservoir particle migration damage primarily include surface deposition or adsorption, bridging or compression deformation at pore throats, and internal pore agglomeration. A key factor in reservoir damage is the shedding of reservoir particles from pore walls under pressure or intrusion of external fluids. These particles migrate with the pore fluid to the pore throat, where they become trapped and deposited, ultimately clogging the reservoir and severely impacting oil and gas production capacity. Therefore, establishing efficient and accurate experimental methods for testing particle migration in unconsolidated sandstone reservoirs and accurately understanding the mechanisms of particle migration damage are crucial for achieving efficient reservoir development and utilization.

[0003] In the field of loose sandstone sample processing, the commonly used methods include encapsulation methods such as glue coating and metal sleeve method. Since the colloid can easily invade the sample gap and contaminate the sample, and is not resistant to solvent cleaning, it directly affects the pore structure of the sample. To ensure the integrity of cores, several core preparation methods have been developed, primarily using sealing methods for mined cores. For example, Xu Jianjun et al., in "A Study on a Sampling Method for Unconsolidated Sandstone Cores," describe four sealing methods: sealing with a lead sleeve, sealing with polytetrafluoroethylene tape alone, sealing with a combination of polytetrafluoroethylene tape and a lead sleeve, and wax boiling. For example, Li Haijiang et al., in "A Brief Discussion on Special Core Sample Preparation Techniques," describe using liquid nitrogen freezing to obtain rock samples from unconsolidated sandstones and then encapsulating the frozen samples to ensure core integrity during experiments. Encapsulation involves wrapping the core with a polytetrafluoroethylene liner, placing a permeable mesh, a pressure ring, and heat shrink tubing over an alcohol lamp until the core is fully shrunken and secure. None of these methods consider the potential for collapse of unconsolidated cores during oil washing, and they are unable to accurately measure the impact of particle migration on reservoir cores. Summary of the Invention

[0004] The present invention is proposed to solve the problems in the prior art of poor cementation of ultra-loose sandstone and easy deformation of pore structure in experiments. Its purpose is to provide a method for preparing ultra-loose sandstone samples and testing long-distance migration of particles.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing ultra-loose sandstone samples and testing long-distance particle migration includes the following steps:

[0007] S1. Freeze the core samples at -15℃~-5℃;

[0008] S2, setting double-layer plugging at both ends of the core sample after being frozen in step S1;

[0009] S3, placing a polyethylene heat shrink sleeve on the outer surface of the structure obtained in step S2, heating the polyethylene heat shrink sleeve so that the polyethylene heat shrink sleeve shrinks and wraps around the core sample and the double-layer seals at both ends to obtain a wash oil sample;

[0010] S4, placing the wash oil sample prepared in step S3 into a Soxhlet extractor for oil washing;

[0011] S5, drying the washed oil sample after washing, and setting an elastic shrinkage device at the injection end of the washed oil sample after washing to obtain a displacement sample;

[0012] S6. Place the displacement sample obtained in step S5 into a displacement device, displace the displacement sample with configured formation water, collect primary produced water from the production end until no more particles are produced, and measure the particle size distribution of the particles in the primary produced water;

[0013] S7. Re-inject the primary produced water collected in step S6 into the displacement sample, collect the secondary produced water at the production end until no more particles are produced, and test the particle size distribution of the secondary produced water after reinjection, that is, obtain the long-distance particle migration law.

[0014] In the above technical solution, the diameter of the core sample in step S1 is 2.5 cm. The core sample is an ultra-loose sandstone core sample drilled from a full-diameter core, containing formation crude oil and retaining the original pore structure.

[0015] In the above technical solution, the freezing treatment condition of step S1 is: freezing at a low temperature for 5 hours to 10 hours, so that the core sample is cylindrical in the frozen state.

[0016] In the above technical solution, the double-layer sealing includes an inner layer of non-magnetic fine yarn mesh and an outer layer of porous polyethylene gasket.

[0017] In the above technical solution, the inner layer of non-magnetic fine yarn mesh is 300-400 mesh, and the mesh diameter of the fine yarn mesh is equal to the median value of the core particle size.

[0018] In the above technical solution, both ends of the polyethylene heat shrink sleeve sleeved on the outside of the structure obtained in step S2 in step S3 extend 2.5 cm to 3 cm beyond the corresponding ends of the structure obtained in step S2.

[0019] In the above technical solution, the heating in step S3 is performed by blowing with a hot air gun, and the hot air gun blowing process ensures that the polyethylene heat shrink sleeve is evenly heated all around, so that the polyethylene heat shrink sleeve tightly wraps the core sample and the double-layer seal at both ends.

[0020] In the above technical solution, in step S4, the Soxhlet extractor uses kerosene as the washing oil medium, the temperature is set according to the shrinkage rate of the heat shrink sleeve, and the temperature is slowly heated using a temperature control instrument.

[0021] The beneficial effects of the present invention are:

[0022] The present invention provides a method for preparing ultra-loose sandstone samples and testing long-distance migration of particles. Based on ultra-loose sandstone samples, the invention takes into account factors such as poor cementation, loose structure and low strength of ultra-loose sandstone, and designs the wrapping preparation of the core to prevent the core from collapsing and becoming deformed due to the washing out of crude oil during the oil washing process. The invention optimizes the method for core collapse at the outlet end of the loose sandstone during the displacement process, and eliminates the particle test under the influence of core collapse of the loose sandstone core during long-term water flooding, so that the study of particle migration law is more accurate. The invention is applied in a high-precision particle migration law test experiment in a water-flooded oil reservoir, which is of great significance for the economic and efficient development and utilization of the oil reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the method of the present invention;

[0024] Figure 2 Schematic diagram comparing the method of the present invention and conventional testing methods.

[0025] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0027] Example 1

[0028] like Figure 1 As shown, a method for preparing ultra-loose sandstone samples and testing long-distance particle migration includes the following steps:

[0029] S1. Drilling core samples: 2.5 cm diameter ultra-loose sandstone core samples containing formation crude oil and retaining the original pore structure were drilled from the full-diameter core under liquid nitrogen freezing conditions. Drilling the core samples under liquid nitrogen freezing conditions is to prevent the core from collapsing and becoming shapeless during the drilling process.

[0030] S2. Freezing the core sample: Freeze the core sample obtained in step S1 at a low temperature of -15°C to -5°C for 5 to 10 hours, so that the core sample is cylindrical in the frozen state;

[0031] S3, setting double-layer plugging at both ends of the core sample after being frozen in step S2;

[0032] The double-layer sealing comprises an inner layer of non-magnetic fine yarn mesh and an outer layer of porous polyethylene gasket.

[0033] The inner layer of non-magnetic fine yarn mesh is 300-400 meshes, and the mesh diameter of the fine yarn mesh is equal to the median value of the core particle size.

[0034] S4, placing a polyethylene heat shrink sleeve on the outer surface of the structure obtained in step S3, heating the polyethylene heat shrink sleeve so that the polyethylene heat shrink sleeve shrinks and wraps around the core sample and the double-layer seals at both ends to obtain a wash oil sample;

[0035] The heating is carried out by blowing with a hot air gun, and the blowing process of the hot air gun ensures that the polyethylene heat shrink sleeve is evenly heated all around, so that the polyethylene heat shrink sleeve, the rock core sample, the fine gauze at both ends and the porous fixing sheets are tightly wrapped, and a fixed rock sample with self-cementing properties is obtained;

[0036] S5, placing the wash oil sample prepared in step S4 into a Soxhlet extractor for oil washing;

[0037] The tightly wrapped and shaped rock sample prepared in step S5 is placed in an extractor. Kerosene is used as an oil washing medium in the extractor. The temperature is set according to the shrinkage rate of the heat shrink sleeve. The heat is slowly heated using a temperature control instrument. As the crude oil is washed out, the heat shrink sleeve further shrinks due to the heat. As a result, the rock particles become less bonded due to the washing out of the crude oil, and the core that is easily deformed and collapsed is reshaped, thereby obtaining a core sample after oil washing;

[0038] S6. Drying the washed oil sample after washing the oil, and setting an elastic shrinkage device at the injection end of the washed oil sample after washing the oil to obtain a displacement sample;

[0039] During the experiment, the elastic shrinkage device always provides a squeezing force to the core sample after oil washing, so that the porous fixing plate at the core outlet is close to the end surface of the core sample after oil washing, supporting the displacement sample and preventing collapse during the displacement process.

[0040] S7. Place the displacement sample obtained in step S6 into a displacement device, displace the displacement sample with configured formation water, collect primary produced water from the production end until no more particles are produced, and measure the particle size distribution of the particles in the primary produced water;

[0041] After the oil washing and drying is completed, a displacement experiment is carried out. Due to the poor cementation, loose structure and low strength of ultra-loose sandstone, the displacement process is often accompanied by the shedding and migration of particles and the occurrence of collapse at the outlet, making it impossible to obtain accurate particle migration patterns. The core is placed in a core holder and a displacement experiment is carried out. The particles in the outflow are collected and monitored. The experiment is suspended when the outflow does not contain any particles.

[0042] S8. Re-inject the primary produced water collected in step S7 into the displacement sample, collect the secondary produced water at the production end, until no more particles are produced, and test the particle size distribution of the secondary produced water after reinjection, that is, obtain the long-distance particle migration law.

[0043] In step S8, the collected outflow water is reinjected into the core. At this time, the rock particles caused by collapse will stay in the cavity formed between the elastic shrinkage device at the inlet end and the experimental core. The particles that migrated long distances inside the core will be eliminated again. The outflow water at this time is collected for testing to obtain accurate long-distance particle migration patterns.

[0044] Through Table 1 and Figure 2 It can be seen that, by comparing the ultra-loose sandstone sample preparation and long-distance particle migration test method of the present invention with the conventional test method, the particle size detected by the method of the present invention is more precise, the result value is relatively accurate, and is not affected by core collapse; the conventional test method is affected by core collapse, and some larger particles are driven out, affecting the test results and causing the result value to be biased larger.

[0045] Table 1: Comparison between the method of the present invention and conventional methods

[0046]

[0047] The present invention specifically designs ultra-loose cores as oil-washing and displacement samples, preserving their original pore structure to the greatest extent possible during testing, enabling precise measurement of the size distribution of particles migrating over long distances within the formation. Ultra-loose sandstone oil-washing samples are prepared using the principle of polytetrafluoroethylene heat shrinkage, allowing rock particles to remain in place during the oil-washing process. Elastic shrinkage devices are then added to the oil-washing samples to create ultra-loose sandstone displacement samples, which are then displaced using formation water. Finally, the particle size distribution in the primary produced water and the secondary produced water after reinjection is tested to determine the size of particles migrating over long distances. This method avoids the impact of ultra-loose core collapse and deformation on experimental results, facilitating accurate optimization of development parameters in oil fields.

[0048] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing ultra-loose sandstone samples and testing long-distance particle migration, characterized by: The following steps are involved: S1, frozen core samples; S2, setting double-layer plugging at both ends of the core sample after being frozen in step S1; S3, placing a polyethylene heat shrink sleeve on the outer surface of the structure obtained in step S2, heating the polyethylene heat shrink sleeve so that the polyethylene heat shrink sleeve shrinks and wraps around the core sample and the double-layer seals at both ends to obtain a wash oil sample; S4, placing the wash oil sample prepared in step S3 into a Soxhlet extractor for oil washing; S5, drying the washed oil sample after washing, and setting an elastic shrinkage device at the injection end of the washed oil sample after washing to obtain a displacement sample; S6. Place the displacement sample obtained in step S5 into a displacement device, displace the displacement sample with configured formation water, collect primary produced water from the production end until no more particles are produced, and measure the particle size distribution of the particles in the primary produced water; S7. Re-inject the primary produced water collected in step S6 into the displacement sample, collect the secondary produced water at the production end until no more particles are produced, and test the particle size distribution of the secondary produced water after reinjection, that is, obtain the long-distance particle migration law.

2. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1, characterized in that: The diameter of the core sample in step S1 is 2.5 cm. The core sample is an ultra-loose sandstone core sample drilled from a full-diameter core, containing formation crude oil and retaining the original pore structure.

3. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1, characterized in that: The freezing treatment conditions in step S1 are: freezing at -15°C to -5°C for 5 hours to 10 hours, so that the core sample is cylindrical in the frozen state.

4. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1, characterized in that: The double-layer sealing comprises an inner layer of non-magnetic fine yarn mesh and an outer layer of porous polyethylene gasket.

5. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 4, characterized in that: The inner layer of non-magnetic fine yarn mesh is 300-400 meshes, and the mesh diameter of the fine yarn mesh is equal to the median value of the core particle size.

6. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1, characterized in that: Both ends of the polyethylene heat shrink sleeve that is sleeved on the outside of the structure obtained in step S2 in step S3 extend 2.5 cm to 3 cm beyond the corresponding ends of the structure obtained in step S2.

7. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1, characterized in that: In step S3, heating is performed by blowing with a hot air gun, and the blowing process with the hot air gun ensures that the polyethylene heat shrink sleeve is evenly heated all around, so that the polyethylene heat shrink sleeve tightly wraps the core sample and the double-layer seals at both ends.

8. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1, characterized in that: In step S4, the Soxhlet extractor uses kerosene as a washing oil medium, sets the temperature according to the shrinkage rate of the heat shrink sleeve, and slowly heats using a temperature control instrument.

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